Histocompatibility methods

De Novo Donor-Specific Antibodies after Heart Transplantation: A Comprehensive Guide for Clinicians

Antibodies directed against donor-specific human leukocyte antigens (HLAs) can be detected de novo after heart transplantation and play a key role in long-term survival. De novo donor-specific antibodies (dnDSAs) have been associated with cardiac allograft vasculopathy, antibody-mediated rejection, and mortality. Advances in detection methods and international guideline recommendations have encouraged the adoption of screening protocols among heart transplant units. However, there is still a lack of consensus about the correct course of action after dnDSA detection. Treatment is usually started when antibody-mediated rejection is present; however, some dnDSAs appear years before graft failure is detected, and at this point, damage may be irreversible. In particular, class II, anti-HLA-DQ, complement binding, and persistent dnDSAs have been associated with worse outcomes. Growing evidence points towards a more aggressive management of dnDSA. For that purpose, better diagnostic tools are needed in order to identify subclinical graft injury. Cardiac magnetic resonance, strain techniques, or coronary physiology parameters could provide valuable information to identify patients at risk. Treatment of dnDSA usually involves plasmapheresis, intravenous immunoglobulin, immunoadsorption, and ritxumab, but the benefit of these therapies is still controversial. Future efforts should focus on establishing effective treatment protocols in order to improve long-term survival of heart transplant recipients.

PD-L1's Role in Preventing Alloreactive T Cell Responses Following Hematopoietic and Organ Transplant

Over the past decade, Programmed Death-Ligand 1 (PD-L1) has emerged as a prominent target for cancer immunotherapies. However, its potential as an immunosuppressive therapy has been limited. In this review, we present the immunological basis of graft rejection and graft-versus-host disease (GVHD), followed by a summary of biologically relevant molecular interactions of both PD-L1 and Programmed Cell Death Protein 1 (PD-1). Finally, we present a translational perspective on how PD-L1 can interrupt alloreactive-driven processes to increase immune tolerance. Unlike most current therapies that block PD-L1 and/or its interaction with PD-1, this review focuses on how upregulation or reversed sequestration of this ligand may reduce autoimmunity, ameliorate GVHD, and enhance graft survival following organ transplant.

Clinical approach to antibody-mediated rejection from the pediatric heart transplant society

This document is designed to outline the definition, pathogenesis, diagnostic modalities and therapeutic measures to treat antibody-mediated rejection in children postheart transplant METHODS: Literature review was conducted by a Pediatric Heart Transplant Society (PHTS) working group to identify existing pediatric and adult studies on antibody-mediated rejection (AMR). In addition, the centers participating in PHTS were asked to submit their approach to diagnosis and management of pediatric AMR. This document synthesizes information gathered from both these sources to highlight a practical approach to diagnosing and managing a child with AMR postheart transplant. This document may not represent the practice at all centers in the PHTS and serves as a starting point to understand an approach to this clinical scenario.

Immunosuppressant Drugs and Their Effects on Children Undergoing Solid Organ Transplant

More than 112,000 men, women, and children are awaiting solid organ transplant (SOT) as of March 2020, and more than 39,000 transplants were performed in the United States in 2019. Approximately 2,000 children undergo SOT every year in the United States, and the number of children awaiting SOT continues to increase. Immunosuppression is the mainstay of prevention and treatment of solid organ rejection, a significant source of morbidity and mortality after SOT. There are several different classes of immunosuppressive drugs, and the phases of immunosuppression after SOT can be divided into early, maintenance, and rescue therapies. The specific class and dose of drug will be determined by the type of organ transplant, time since transplant, phase of therapy, and other patient-specific considerations. The goal of the transplant team is to find the optimal balance between too little immunosuppression and too much immunosuppression. Too little immunosuppression can result in organ rejection, but too much immunosuppression can result in increased infections, increased malignancy, and adverse drug events such as nephrotoxicity. Although the specific drug choice and dosage will be managed by specialized transplant physicians, these immunosuppressive drugs have many drug interactions with commonly prescribed medications and require dose titration. To provide the best care to children who have received a SOT, pediatricians should be aware of these interactions and be able to distinguish routine pediatric concerns from transplant immunosuppression-related infections or complications. Current vaccine recommendations for children receiving immunosuppression after SOT are also discussed.

Aspects of histocompatibility testing in xenotransplantation

Xenotransplantation, using genetically-modified pigs for clinical organ transplantation, is a solution to the organ shortage. The biggest barrier to clinical implementation is the antigenicity of pig cells. Humans possess preformed antibody to pig cells that initiate antibody-mediated rejection of pig organs in primates. Advances in genetic engineering have led to the development of a pig lacking the three known glycan xenoantigens (triple-knockout [TKO] pigs). A significant number of human sera demonstrate no antibody binding to TKO pig cells. As a result of the TKO pig's low antigen expression, survival of life-supporting pig organs in immunosuppressed nonhuman primates has significantly increased, and hope has been renewed for clinical trials of xenotransplantation. It is important to understand the context in which xenotransplantation's predecessor, allotransplantation, has been successful, and the steps needed for the success of xenotransplantation. Successful allotransplantation has been based on two main immunological approaches - (i) adequate immunosuppressive therapy, and (ii) careful histocompatibility matching. In vivo studies suggest that the available immunosuppressive regimens are adequate to suppress the human anti-pig cellular response. Methods to evaluate and screen patients for the first clinical xenotransplantation trial are the next challenge. The goal of this review is to summarize the history of histocompatibility testing, and the available tools that can be utilized to determine xenograft histocompatibility.

Phasing out the pre-transplant cytotoxicity crossmatch: Are we missing something?

Introduction:

The anti-human globulin-enhanced complement-dependent cytotoxicity crossmatch (AHG-CDCXM) assay has been used to assess the presence of donor-specific antibodies (DSA) in recipient’s serum before kidney transplantation. The flow cytometric crossmatch (FCXM) assay was first introduced as an additional test. The aim of this study was to clinically validate the single use of the FCXM assay.

Methods:

This study compared the outcomes of a cohort of kidney transplant patients that underwent FCXM only (FCXM group) versus a cohort of kidney transplant patients that underwent AHG-CDCXM (control group).

Results:

Ninety-seven patients in the FCXM group and 98 controls were included. All crossmatches in the control group were negative. One patient in the FCXM group had a positive B cell crossmatch. One year after transplantation, there were no significant differences in patient survival (p = 0.591) and graft survival (p = 0.692) between the groups. Also, no significant difference was found in the incidence of Banff ≥ 1A acute cellular rejection episodes (p = 0.289). However, acute antibody-mediated rejections occurred in 3 controls (p = 0.028).

Conclusion:

The results showed that discontinuing the AHG-CDCXM assay does not modify the clinical outcomes in a 1-year follow-up.

The Role of SLAs in Xenotransplantation

Advances in genetic engineering, particularly CRISPR/Cas9, have resulted in the development of a triple glycan-knockout (TKO) pig. There is minimal human antipig antibody binding to TKO pig cells. The TKO background has decreased antibody binding to a sufficiently low level that any additional xenoantigens expressed on the cells can now be more easily detected. One of these xenoantigens is the swine major histocompatibility complex, termed swine leukocyte antigens (SLA). SLA are the homolog to HLAs, a protein complex expressed on human tissue capable of stimulating the development of new antibodies in allotransplantation. These antibodies can result in graft failure through hyperacute, acute, or chronic rejection. Our knowledge of SLA, particularly in the last 5 years, has grown considerably. The presence, cause, and methods to detect anti-SLA antibodies will need to be carefully considered for the first clinical trial of xenotransplantation. The focus of this review is to summarize the role of SLA in xenotransplantation and consider whether it will prove to be a major barrier. Techniques are now available to mutate target SLA amino acids to ensure that cross-reactive anti-HLA antibodies no longer bind to SLA on the cells of the organ-source pigs. While deletion of SLA expression is possible, it would render the pig at risk for infectious complications. The ideal organ-source pig for HLA highly sensitized recipients may therefore be 1 with site-specific mutations to eliminate cross-reactive binding.

Matchmaker, matchmaker make me a match: Opportunities and challenges in optimizing compatibility of HLA eplets in transplantation

The development of donor-specific antibodies (DSAs) is a major complication in transplantation, which is associated with inferior graft survival, impaired quality of life, and increased healthcare costs. DSA develop upon recognition of nonself HLA by the recipient's immune system. HLA molecules contain epitopes, which are the surface regions of HLA molecules recognized by antibodies. HLAMatchmaker is an algorithm for assessing donor:recipient HLA compatibility at the level of structurally defined HLA targets called eplets. The consideration of eplets, rather than the whole HLA molecule, could offer some advantages when classifying the immune risk associated with particular donor:recipient pairs. Assessing compatibility at the level of HLA eplets could decrease misclassification of post-transplant immune risk by improving specificity, when antibodies are confirmed to be directed against donor eplets missing from the recipient's repertoire of eplets. Consideration of eplets may also increase the sensitivity of immune risk assessment, when identifying mismatched eplets that could give rise to new, not previously detected, donor-specific antibodies post-transplant. Eplet matching can serve as a rational strategy for immune risk mitigation. Herein, we review the evolution of HLA (in) compatibility assessment for organ allocation. We outline challenges in the implementation of eplet-based donor:recipient matching, including unavailability of allele-level donor genotypes for 11 HLA loci at the time of organ allocation and difficulty in assessing the hierarchy of immune risk associated with particular HLA eplet mismatches. Opportunities to address some of the current shortcomings of donor genotyping and HLAMatchmaker are also discussed. While there is a demonstrated benefit in the application of HLAMatchmaker for donor: recipient HLA (in)compatibility assessment, evolving long-read genotyping methods, compilation of large data sets with allele-level genotypes, and standardization of methods to verify eplets as determinants of immune-mediated injuries are required before HLA eplet matching is implemented in organ allocation to improve upon transplant outcomes.

HLA Alloimmunization Following Ventricular Assist Device Support Across the Age Spectrum

BACKGROUND

Ventricular assist device (VAD) therapy has become an important tool for end-stage heart failure. VAD therapy has increased survival but is associated with complications including the development of human leukocyte antigen (HLA) antibodies. We sought to determine the incidence of HLA antibody development post-VAD insertion, across the age spectrum, in patients receiving leukocyte-reduced blood products, with standardized HLA antibody detection methods and to investigate factors associated with antibody development.

METHODS

This was a retrospective analysis of all patients who underwent durable VAD placement between 2005 and 2014. Inclusion criteria included availability of pre- and post-VAD HLA antibody results. Associations between HLA antibody development in the first-year postimplant and patient factors were explored.

RESULTS

Thirty-nine adult and 25 pediatric patients made up the study cohort. Following implant, 31% and 8% of patients developed new class I and class II antibodies. The proportion of newly sensitized patients was similar in adult and pediatric patients. The class I HLA panel reactive antibody only significantly increased in adults. Pre-VAD sensitization, age, sex (pediatrics), and transfusion were not associated with the development of HLA antibodies.

CONCLUSIONS

In a cohort of VAD patients receiving leukocyte-reduced blood products and standardized HLA antibody testing, roughly one-third developed new class I antibodies in the first-year postimplant. Adults showed significantly increased class I panel reactive antibody following VAD support. No patient-related factors were associated with HLA antibody development. Larger prospective studies are required to validate these findings and determine the clinical impact of these antibodies following VAD insertion.

[Renal transplantation: Procedure and early follow-up]

More than fifty years after the success of the two first renal transplantations in Boston and in Necker hospital in Paris, renal transplantation became the treatment of choice of end stage renal failure, because it improves not only the quality of life of the patients but also their long-term survival. In France, more than 3,700 kidney transplantations are performed every year and more than 40,000 patients are living with a functioning kidney allograft. This treatment of end stage renal disease requires a fine-tuned pre-transplant evaluation and a multidisciplinary post-transplant care in order to prevent, to detect and to treat comorbidities and complications of immunosuppression. The ambition of this manuscript is not to describe in an exhaustive way all the aspects of renal transplantation but starting from the experience of a team, recently published data, and national and international guidelines, to try to provide a synthetic and chronological view of the early post-transplant monitoring.

HLA in transplantation

The human major histocompatibility complex is a family of genes that encodes HLAs, which have a crucial role in defence against foreign pathogens and immune surveillance of tumours. In the context of transplantation, HLA molecules are polymorphic antigens that comprise an immunodominant alloreactive trigger for the immune response, resulting in rejection. Remarkable advances in knowledge and technology in the field of immunogenetics have considerably enhanced the safety of transplantation. However, access to transplantation among individuals who have become sensitized as a result of previous exposure to alloantigens is reduced proportional to the breadth of their sensitization. New approaches for crossing the HLA barrier in transplantation using plasmapheresis, intravenous immunoglobulin and kidney paired donation have been made possible by the relative ease with which even low levels of anti-HLA antibodies can now be detected and tracked. The development of novel protocols for the induction of tolerance and new approaches to immunomodulation was also facilitated by advances in HLA technology. Here, we review the progress made in understanding HLAs that has enabled organ transplantation to become a life-saving endeavour that is accessible even for sensitized patients. We also discuss novel approaches to desensitization, immunomodulation and tolerance induction that have the potential to further improve transplantation access and outcomes.

Luminex Solid-Phase Crossmatch for De Novo Donor-Specific Antibodies in Living-Donor Related Transplants

OBJECTIVES

There are no reports of de novo donor-specific antibody monitoring by a low-cost solid-phase crossmatch assay using donor lysate after renal transplant.

MATERIALS AND METHODS

We prospectively evaluated 121 complement-dependant cytotoxicity crossmatch-negative living-donor kidney transplant recipients for development of de novo donor-specific antibodies (class I and II HLA) by solid-phase crossmatch Luminex assay after transplant.

RESULTS

Of 121 recipients in our study group, 26 (21.5%) developed de novo donor-specific antibody within 3 months after transplant. Fifteen (58%) of these 26 recipients developed class II de novo donor-specific antibody, 8 patients (30%) developed class I, and 3 (12%) developed both class I and class II. Of the remaining 95 patients (79%) who did not develop de novo donor-specific antibody, 6 (33.3%) had antibody-mediated rejection with glomerulitis (2 with C4d-positive disease). Donor-specific antibody was detected by Luminex solid-phase crossmatch in 18 patients (5 with class I, 11 with class II, and 2 with both class I and II), all with no evidence of clinical rejection. Development of de novo donor-specific antibody detected by solid-phase crossmatch was associated with more acute rejection (31% in de novo donor-specific antibody-positive group versus 19% in the negative group). The positive group had more antibody-mediated rejection (75% of acute rejections), whereas only 33.3% of acute rejections in the negative group were antibody-mediated rejection. Of 12 patients with antibody-mediated rejection, 9 were C4d negative (75%) and were diagnosed by donor-specific antibody positivity detected by solid-phase cros?match testing and histologic findings. The use of donor lysate in solid-phase crossmatch assays is more economical than the single-antigen bead Luminex assay (per test cost of US $45.20 vs $403.20).

Changing Paradigms in the Management of Rejection in Kidney Transplantation: Evolving From Protocol-Based Care to the Era of P4 Medicine

PURPOSE OF REVIEW

P4 medicine denotes an evolving field of medicine encompassing predictive, preventive, personalized, and participatory medicine. Using the example of kidney allograft rejection because of donor-recipient incompatibility in human leukocyte antigens, this review outlines P4 medicine's relevance to the various stages of the kidney transplant cycle.

SOURCES OF INFORMATION

A search for English articles was conducted in Medline via OvidSP (up to August 18, 2016) using a combination of subject headings (MeSH) and free text in titles, abstracts, and author keywords for the concepts kidney transplantation and P4 medicine. The electronic database search was expanded further on particular subject headings.

FINDINGS

Available histocompatibility methods exemplify current applications of the predictive and preventive domains of P4 medicine in kidney transplant recipients' care. Pharmacogenomics are discussed as means to facilitate personalized immunosuppression regimens and promotion of active patient participation as a means to improve adherence.

LIMITATIONS

For simplicity, this review focuses on rejection. P4 medicine, however, should more broadly address health concerns in kidney transplant recipients, including competing outcomes such as infections, malignancies, and cardiovascular disease. This review highlights how biomarkers to evaluate these competing outcomes warrant validation and standardization prior to their incorporation into clinical practice.

IMPLICATIONS

Consideration of all 4 domains of the P4 medicine framework when caring for and/or studying kidney transplant recipients has the potential of increasing therapeutic efficiency, minimizing adverse effects, decreasing health care costs, and maximizing wellness. Technologies to gauge immune competency, immunosuppression requirements, and early/reversible immune-mediated injuries are required to optimize kidney transplant care.

Current status on the evaluation and management of the highly sensitized kidney transplant recipient

PURPOSE OF REVIEW

In light of the recent changes to the kidney allocation system (KAS) and the observed increase in the rate of transplantation of the highly sensitized kidney transplant candidate, the evaluation and care of this population is a timely topic.

RECENT FINDINGS

In its first year, the new KAS has already realized one goal of improving the chances of transplanting the most highly sensitized patients in the waiting list. This has brought to the forefront the need for recipient readiness in this special population, as well as the need for histocompatibility labs and kidney transplant programs to align themselves with each other, and also with the requirements of the United Network for Organ Sharing, and increase proficiency in testing and data interpretation. This manuscript is a review of the literature as well as practice patterns as they relate to the changes in KAS and the observed outcome since the activation of the new KAS, with the ultimate goal of aiding in the development of a more unified approach in the care of this specialized population which will allow for interdisciplinary and cross centre dialogue to optimize long term care and outcomes.

SUMMARY

Here we will review the changes to the KAS as they affect the highly sensitized kidney transplant recipient, and additional considerations in the evaluation and management of these patients.

Translational research in kidney transplantation and the role of patient engagement

Background

Translational research is an evolving discipline that is intended to bridge the gaps between basic science research, clinical research, and implementation in clinical practice. It is a fluid, multidirectional process that requires strong interdisciplinary collaboration to produce research that is relevant to end-users.

Purpose of this review

This review summarizes current perspectives on translational research and outlines its relevance and importance to kidney transplantation research.

Sources of information

Sources of information used for this review include published reports, articles, and research funding websites.

Findings

Tissue typing is used as an in-depth example of how translational research has been applied in the field of kidney transplant medicine, and how it has resulted in successful implementation of diagnostic and management options for sensitized individuals undergoing kidney transplantation. The value of actively involving kidney transplant stakeholders (patients, caregivers, and clinicians) in setting research priorities and determining relevant outcomes for future investigation is also discussed.

Limitations

This is a narrative review of the literature which has been partly influenced by the perspectives and experiences of its authors.

Implications

Translational and patient-oriented research practices should be incorporated into future research endeavours in the field of kidney transplantation in order to create beneficial change in clinical practice and improve patient outcomes.

What was known before

Translational research which engages patients in the investigative process can enhance the likelihood that medical discoveries will have a meaningful impact at the bedside.

What this adds

This article applies current perspectives on translational research and patient engagement to the field of kidney transplantation, illustrating how these approaches have led to significant advancements in the field. It provides further justification for deliberate, targeted efforts to cross-collaborate and incorporate the patient voice into kidney transplant research.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

HLA-DR and -DQ eplet mismatches and transplant glomerulopathy: a nested case-control study

We conducted a nested case-control study from a cohort of adult kidney transplant recipients to assess the risk of transplant glomerulopathy (TG) as a function of donor and recipient HLA-DR and -DQ incompatibility at the eplet level. Cases (n = 52) were defined as patients diagnosed with transplant glomerulopathy based on biopsies showing glomerular basement membrane duplication without immune complex deposition. Controls (n = 104) with a similar follow-up from transplantation were randomly selected from the remaining cohort. HLAMatchmaker was used to ascertain the number of DRB1/3/4/5, DQA1 and DQB1 related eplet mismatches (eplet load). Multivariable conditional logistic regression models demonstrated an increase in the odds of TG (odds ratios [OR] of 2.84 [95% confidence interval (CI): 1.03, 7.84] and 4.62 [95% CI: 1.51, 14.14]) in the presence of 27-43 and >43 HLA-DR + DQ related eplet mismatches versus <27 eplet mismatches, respectively. When the eplet load was modeled as a continuous variable, the OR for TG was 1.25 (95% CI: 1.04, 1.50) for every 10 additional HLA-DR + DQ eplet mismatches. Our study suggests that minimization of HLA-DR + DQ eplet mismatches may decrease the incidence of transplant glomerulopathy diagnosed by indication biopsies. The role of eplet immunogenicity/antigenicity as determinants of allograft outcomes requires further study.

A systematic review of the role of C4d in the diagnosis of acute antibody-mediated rejection

In this study, we conducted a systematic review of the literature to re-evaluate the role of C4d in the diagnosis of acute antibody-mediated rejection of kidney allografts. Electronic databases were searched until September 2013. Eligible studies allowed derivation of diagnostic tables for the performance of C4d by immunofluorescence or immunohistochemistry with comparison to histopathological features of acute antibody-mediated rejection and/or donor-specific antibody (DSA) assays. Of 3492 unique abstracts, 29 studies encompassing 3485 indication and 868 surveillance biopsies were identified. Assessment of C4d by immunofluorescence and immunohistochemistry exhibited slight to moderate agreement with glomerulitis, peritubular capillaritis, solid-phase DSA assays, DSA with glomerulitis, and DSA with peritubular capillaritis. The sensitivity and specificity of C4d varied as a function of C4d and comparator test thresholds. Prognostically, the presence of C4d was associated with inferior allograft survival compared with DSA or histopathology alone. Thus, our findings support the presence of complement-dependent and -independent phenotypes of acute antibody-mediated rejection. Whether the presence of C4d in combination with histopathology or DSA should be considered for the diagnosis of acute antibody-mediated rejection warrants further study.

Challenges with sensitized recipients in pediatric heart transplantation

The sensitization of patients to human leukocyte antigens prior to heart transplantation is increasingly being recognized as an important challenge both before and after the transplant, and the effects of sensitization on clinical outcomes are just beginning to be understood. Many patients are listed with the requirement of a negative prospective or virtual crossmatch prior to accepting a donor organ. This strategy has been associated with both longer waitlist times and higher waitlist mortality. An alternative approach is to transplant across a potentially positive crossmatch while utilizing strategies to decrease the significance of the human leukocyte antigen antibodies. This review will examine the challenges and the impact of sensitization on pediatric patients prior to and following heart transplantation.

Comparision of anti-HLA antibodies of kidney transplant candidates with chronic renal failure by two different methods: Flow-PRA and Luminex PRA

OBJECTIVE

The aim of the study was to compare anti-HLA antibodies examined as panel-reactive antibody (PRA) in kidney transplant candidates with chronic renal failure (CRF) with the use of 2 methods: Flow-PRA and Luminex-PRA.

METHODS

CRF patients displaying class I PRA (n = 34) and/or class II PRA (n = 41) were tested by the 2 different methods from April 2012 to September 2012, using antigen-coated beads.

RESULTS

Eleven (32.3%) 34 patients tested for class I PRA were female and 23 (67.7%) male; 17 (41.5%) 41 patients tested for class II PRA were female and 24 (58.5%) male. Only 2 patients were preemptive, the others had been subjected to dialysis. The concordance ratio of class I PRA test results between Flow-PRA and Luminex PRA was 67.6%. Whereas 13 samples (38.2%) were positive by Flow-PRA, 22 (64.7%) were positive by Luminex-PRA. Two of the 3 patients not previously immunized were found to be positive only by Luminex PRA; 1 was noted to be positive only by Flow-PRA. Regarding class II PRA screening, the concordance between Flow-PRA and Luminex PRA was 70.7%. Whereas 14 (34.1%) samples were positive for Flow-PRA; 24 (58.5%) were positive for Luminex-PRA. The 2 patients not previously immunized were positive only in Luminex PRA.

CONCLUSIONS

We speculated that the reason for the low concordance ratios was due to the use of sera that had been previously found to be indeterminate in PRA tests. We also speculated that the low concordance ratios were due to the coating procedure for the beads, which may cause changes in antigenic epitopes and decrease concordance between Flow-PRA and Luminex-PRA.

Comparison of complement-dependent cytotoxic and flow-cytometry crossmatch results before cadaveric kidney transplantation

AIM

The presence of HLA donor-specific antibodies (DSA) before kidney transplantation decreases graft survival. In this study, we compared crossmatch results of kidney transplantation candidates, for cadaveric renal donation between March 10, 2012, and September 7, 2012.

MATERIAL AND METHOD

The 47 kidney transplantation candidates tested for crossmatch included 10 for cadaveric donor organs. Two crossmatch methods were performed: complement-dependent cytotoxic crossmatch (CDCXM) and flow cytometry crossmatch (FCXM). Spleen cells were used as the source of lymphocytes for all crossmatch tests.

RESULTS

The T and B cell ratios isolated from spleen were 38.8% and 34.8%, respectively. The concordance ratio of the two methods was 76.6% with 23.4% discordant results. Regarding the discordant results, 4.2% were positive CDCXM but negative FCXM; 191%, negative CDCXM but positive FCXM. All patients displaying positive crossmatches had a previous immunization history. As a result, we speculated that the positive CDCXM but negative FCXM results were due to the washing procedures in the FCXM disturbing antigen-antibody complexes. We suggest at least two different methods to be performed for crossmatch tests before kidney transplantation. CDCXM detects immunoglobulin G1 (IgG1) and IgG3, which are critical for rejection. FCXM is able to detect all IgG subgroups because of its high sensivity. As a result we suggest that both CDCXM and FCXM are preferrable strategies to detect DSAs.

Antibody-mediated rejection in the liver allograft

PURPOSE OF REVIEW

There is increasing evidence to suggest that antibody-mediated mechanisms play a role in the pathogenesis of liver allograft rejection. This article will review the pathology of antibody-mediated rejection (AMR) focusing on recent studies which have improved our understanding of the clinicopathological features and diagnostic approaches.

RECENT FINDINGS

Recent studies have investigated the patterns of immunohistochemical staining for C4d as a tissue marker of AMR in posttransplant biopsies, and have correlated these findings with other histopathological changes and with the presence of donor-specific antibodies (DSAs). These studies have highlighted the diagnostic applications and limitations of C4d immunostaining. They have also emphasized the importance of using strict criteria for defining 'pure' AMR in the liver allograft - that is, graft dysfunction associated with compatible histological findings (typically resembling biliary obstruction), the presence of DSAs and diffusely positive staining for C4d.

SUMMARY

Pure AMR is relatively uncommon in ABO-compatible grafts - it should be diagnosed on the basis of strict criteria and requires treatment with antibody-depleting immunosuppression. C4d immunostaining in isolation has limited diagnostic value. However, the presence of diffuse C4d immunostaining (involving endothelium or stroma in >50% of portal tracts or sinusoids) suggests a significant component of antibody-mediated graft damage. In a person with suggestive histological features, this finding should prompt testing for DSAs. Even in the absence of typical histological features of AMR, the combined presence of DSAs and diffuse C4d positivity is associated with more frequent or severe acute and chronic rejection, which may also warrant treatment with antibody-depleting immunosuppression.

Effect of high-dose intravenous immunoglobulin on anti-HLA antibodies in sensitized kidney transplant candidates

Limited data exist on the effect of intravenous immunoglobulin (IVIg) on anti-HLA antibodies as determined by solid-phase assays. We reviewed our experience treating sensitized wait-listed kidney transplant recipients with IVIg as a method for desensitization and report our results utilizing Luminex single antigen (LSA) bead assay to quantify antibody reactivity (MFI). Fifteen patients with a cPRA > 40% received 2 g/kg IVIg per month for four months or until transplanted. LSA testing was performed before and after IVIg. Median MFI for anti-class I antibodies fell in 11 (73%) and increased in 4 (27%) patients after IVIg. Similar significant changes in MFI for anti-class II antibodies were observed in 10 patients (66%). Administration of IVIg was associated with a modest decrease in reactivity to both class I and II HLA antigens (median MFI change 493 and 1110, respectively; p < 0.0001) but did not significantly alter mean cPRA (85% before IVIg vs. 80% after IVIg; p = 0.1). Our data suggest a smaller effect of IVIg on HLA antibody reactivity than previously described, leading us to question how best to measure the efficacy of a desensitization protocol in current practice.

HLA techniques: typing and antibody detection in the laboratory of immunogenetics

The HLA loci are a part of the genetic region known as the major histocompatibility complex (MHC). In the last twenty years there has been an exponential growth in the application of DNA technology to the field of histocompatibility and immunogenetics. Histocompatibility between the patient and donor is a prerequisite for the success of haematopoietic stem cell transplantation. In haematopoietic stem cell transplantation allele-level typing needs to evaluate compatibility for the HLA-A,B,C Class I and DRB1 and DQB1 Class II loci in the average transplant program because it is well established that mismatches at certain HLA loci between donor-recipients are closely linked to the risk of graft versus host disease. Resolution at an antigen level in solid organ transplantation is currently sufficient for HLA-A,B and DR antigens and it could be achieved by serological or molecular biology techniques. In solid organ transplantation the definition of antibodies in the recipient to HLA antigens is more important and it was performed primarily by serological technique and more recently by solid phase immunoassays that are more sensitive and specific.

Antibody-mediated rejection: an evolving entity in heart transplantation

Antibody-mediated rejection (AMR) is gaining increasing recognition as a major complication after heart transplantation, posing a significant risk for allograft failure, cardiac allograft vasculopathy, and poor survival. AMR results from activation of the humoral immune arm and the production of donor-specific antibodies (DSA) that bind to the cardiac allograft causing myocardial injury predominantly through complement activation. The diagnosis of AMR has evolved from a clinical diagnosis involving allograft dysfunction and the presence of DSA to a primarily pathologic diagnosis based on histopathology and immunopathology. Treatment for AMR is multifaceted, targeting inhibition of the humoral immune system at different levels with emerging agents including proteasome and complement inhibitors showing particular promise. While there have been significant advances in our current understanding of the pathogenesis, diagnosis, and treatment of AMR, further research is required to determine optimal diagnostic tools, therapeutic agents, and timing of treatment.

Flow cytometric crossmatching and panel-reactive antibodies in chronic renal failure patients

AIM

Anti-donor antibodies, denoted as "panel-reactive antibodies" (PRAs), are one of the most important factors influencing graft survival after renal transplantation. PRA is generally analyzed with enzyme-linked immunosorbent assay or flow cytometry (FC), which identify the HLA antigen specific for the preformed antibody.

PATIENTS AND METHODS

We tested 66 patients for FC crossmatch (FCXM) when they were called for cadaveric renal transplantation. Thirty of 66 patients were FCXM-positive; 36 were FCXM-negative. Among the FCXM positive crossmatches, 21 were T- and B-cell positive; seven B positive; and two T positive. The HLA antibodies in the sera of FCXM-positive patients were reanalyzed using flow-PRA.

RESULTS

We detected HLA antibodies in 28/66 sera with flow PRA. The sera of 16/21 T-/B-, FCXM-positive patients contained both class I and II anti-HLA antibodies, five had only class I anti-HLA antibodies. One out of seven B-cell FCXM-positive patients had class I and class II anti-HLA antibodies, three, class I and 1 class II anti-HLA antibodies; the other two were negative. Class I and class II HLA antibodies were observed in two T-cell FCXM-positive patients. Four of 36 patients who were FCXM-negative were flow PRA positive: one had both class I and class II HLA antibodies and three, only class I HLA antibody. The comparison of FCXM and flow PRA results was significant (P = .001).

CONCLUSION

FCXM results may be confirmed by flow PRA tests, an important method to differentiate HLA versus non-HLA antibodies.